1. Field of the Invention
The present invention relates to a method and apparatus for transmitting and receiving a multimedia broadcast/multicast service (MBMS), and more particularly, to an apparatus and method for transmitting and receiving an MBMS using Automatic Repeat Request (ARC) and Hybrid Automatic Repeat Request (HARQ). Although the present invention is suitable for a wide scope of applications, it is particularly suitable for providing a multicast transmission using adaptive modulation and channel coding and Hybrid ARQ to a wireless mobile user equipment to enable the user equipment to receive high-speed multicast data.
2. Description of the Related Art
FIG. 1 illustrates a block diagram of a network structure of UMTS (Universal Mobile Telecommunications System). A UMTS includes user equipment (hereinafter abbreviated UE), a UMTS terrestrial radio access network (hereinafter abbreviated UTRAN), and a core network (hereinafter abbreviated CN).
The UTRAN includes at least one radio network sub-system (hereinafter abbreviated RNS). The RNS includes one radio network controller (hereinafter abbreviated RNC) and at least one base station (hereinafter called Node B) managed by the RNC. At least one or more cells exist in one Node B.
FIG. 2 illustrates an architectural diagram of a radio interface protocol between one UE and a UTRAN. A radio interface protocol vertically includes a physical layer, a data link layer, and a network layer and horizontally includes a user plane for data information transfer and a control plane for signaling transfer. The protocol layers in FIG. 2 can be divided into L1 (first layer), L2 (second layer) and L3 (third layer) based on three lower layers of the open system interconnection (OSI) standard model widely known in the communications systems.
The physical layer (hereinafter named PHY) offers information transfer services to an upper layer using physical channels. The physical layer is connected to a medium access control (hereinafter abbreviated MAC) layer above the physical layer via transport channels. Data are transferred between the MAC layer and the PHY layer via a transport channel. Data are transferred between different physical layers, and more specifically, between one physical layer of a transmitting side and the other physical layer of a receiving side via physical channels.
The MAC layer of the second layer offers services to a radio link control layer above the MAC layer via logical channels. The radio link control (hereinafter abbreviated RLC) layer of the second layer supports reliable data transfer and performs segmentation and concatenation of RLC service data units (hereinafter abbreviated SDU) sent down from an upper layer.
A radio resource control (hereinafter abbreviated RRC) layer located on a lowest part of the third layer is defined in the control plane only and is associated with configuration, reconfiguration and release of radio bearers (hereinafter abbreviated RB) for controlling the logical, transport and physical channels. A RB is a service offered to the second layer for the data transfer between the UE and the UTRAN. The configuration of a RB is a process of regulating characteristics of protocol layers and channels necessary for offering a specific service and a process of setting their specific parameters and operational methods, respectively.
A multimedia broadcast/multicast service (hereinafter abbreviated MBMS) offers a streaming or background service to a plurality of UEs using a downlink dedicated MBMS bearer service. One MBMS includes at least one session, and MBMS data are transmitted to a plurality of the UEs via the MBMS bearer service only during an ongoing session.
A UTRAN offers the MBMS bearer service to a UE via a radio bearer. The types of RB used by the UTRAN include a point-to-point radio bearer and a point-to-multipoint radio bearer. A point-to-point radio bearer is a bi-directional radio bearer and includes a logical channel DTCH (dedicated traffic channel), a transport channel DCH (dedicated channel) and a physical channel DPCH (dedicated physical channel) or a physical channel SCCPCH (secondary common control physical channel). A point-to-multipoint radio bearer is a unidirectional downlink radio bearer.
FIG. 3 illustrates channel mapping for MBMS. A point-to-multipoint radio bearer includes a logical channel MTCH (MBMS traffic channel), a transport channel FACH (forward access channel) and a physical channel SCCPCH. The logical channel MTCH is configured for each MBMS offered to one cell and is used in transmitting user-plane data of a specific MBMS to a plurality of UEs.
A logical channel MCCH (MBMS control channel) is a point-to-multipoint downlink channel used in transmitting control information associated with the MBMS. The logical channel MCCH is mapped to the transport channel FACH (forward access channel), while the transport channel FACH is mapped to the physical channel SCCPCH (secondary common control physical channel). One MCCH exists within one cell.
The UTRAN offering the MBMS transmits MCCH information to a plurality of UEs via the MCCH. The MCCH information includes a notification message associated with the MBMS, for example, an RRC message associated with the MBMS. The MCCH information may include a message that indicates MBMS information, a message that notifies point-to-multipoint radio bearer information or access information indicating that an RRC connection is requested for a specific MBMS.
FIG. 4 illustrates a transmission system of MCCH information. The MCCH information is periodically transmitted according to a modification period and a repetition period.
The MCCH information is divided into critical information and non-critical information. The non-critical information can be freely modified each modification period or each repetition period. The modification of the critical information can be made only each modification period. Specifically, the critical information is repeated one time each repetition period and the transmission of the modified critical information is possible at a start point of the modification period only.
The UTRAN periodically transmits a physical channel MICH (MBMS notification indicator channel) to indicate whether the MCCH information is updated during the modification period. Therefore, a UE attempting to receive only one specific MBMS does not receive the MCCH or MTCH until a session of the service begins, but receives MICH (MBMS notification indicator channel) periodically. For reference, the update of the MCCH information means a generation, addition, modification or removal of a specific item of the MCCH information.
FIG. 5 illustrates a flowchart of a process for executing an MBMS according to the related art. Once a session of a specific MBMS begins (S51), a UTRAN transmits an NI (notification indicator) to a UE attempting to receive a specific MBMS (S52). The NI indicates that an MCCH channel should be received. The UE, having received the NI via an MICH, receives an MCCH for a specific modification period indicated by the MICH.
A UE attempting to receive a specific MBMS using a point-to-multipoint radio bearer receives MCCH information including radio bearer information via an MCCH and then configures the point-to-multipoint radio bearer using the received information (S53). After completion of configuring the point-to-multipoint radio bearer, the UE keeps receiving a physical channel SCCPCH, to which an MTCH is mapped, in order to acquire data of the specific MBMS transmitted via the MTCH (S54). If a session ends (S55), the configured point-to-multipoint radio bearer is released (S56).
FIG. 6 illustrates a method of transmitting MBMS data discontinuously via MTCH. A UTRAN periodically transmits a scheduling message to a UE via an SCCPCH (SCCPH carrying MTCH) to which an MTCH is mapped. The scheduling message indicates a transmission start point and transmission section of MBMS data transmitted during one scheduling period. The UTRAN should previously inform the UE of a transmission period (scheduling period) of scheduling information.
The UE acquires the scheduling period from the UTRAN, receives the scheduling message periodically according to the acquired scheduling period, and then receives the SCCPCH (SCCPH carrying MTCH) to which the MTCH is mapped. The SCCPCH is received discontinuously and periodically using the received scheduling message. Specifically, the UE, using the scheduling message, receives the SCCPCH carrying the MTCH during a timing section for which the data is transmitted but does not receive the SCCPCH carrying the MTCH during a time section for which the data is not transmitted. The method is advantageous in that the UE can efficiently receive the data to reduce its battery consumption.
An HS-DSCH transmission of transmitting high-speed data in downlink to one UE is explained as follows.
An HS-DSCH has a 2 ms transmission time interval (hereinafter abbreviated TTI) (3 slot) and supports various modulation code sets (hereinafter abbreviated MCSs) for a high data rate. By selecting an MCS most suitable for a channel status, an optimal throughput is provided. HARQ is adopted to enable a reliable transmission. HARQ involves combining ARQ and channel coding.
FIG. 7 illustrates an HS-DSCH protocol stack according to the related art. A data unit delivered from an RLC layer of a serving radio network controller (hereinafter abbreviated SRNC) is delivered to an MAC-d entity managing a dedicated channel via a logical channel DTCH (dedicated traffic channel) or DCCH (dedicated control channel). The data unit is then passed through a MAC-c/sh/m of a controlling radio network controller (hereinafter abbreviated CRNC) to deliver the corresponding data to a MAC-hs of a Node B. The MAC-d is an entity that manages the dedicated channel. The MAC-c/sh/m is an entity that manages a common channel. The MAC-hs is a MAC entity that manages the HS-DSCH.
A physical channel HS-PDSCH is used for delivering the HS-DSCH, which is a transport channel. A spreading factor of the HS-PDSCH is fixed at 16 and the HS-PDSCH corresponds to one channelization code selected from a channelization code set prepared for a HS-DSCH data transmission. When performing a multi-code transmission for one UE, a plurality of channelization codes are assigned during the same HS-PDSCH sub-frame.
FIG. 8 illustrates a HS-DSCH sub-frame and slot according to the related art. A HS-PDSCH transfers QPSK (Quadrature Phase Shift Keying) or 16-QAM (Quadrature Amplitude Modulation) modulation symbols. In FIG. 8, “M” designates a bit number per modulation symbol. For QPSK, “M” is equal to 2 (M=2) and for 16-QAM, “M” is equal to 4 (M=4).
FIG. 9 illustrates a channel configuration according to the related art. A transmission of HS-DSCH control information is needed to transfer user data via an HS-DSCH. The information is transmitted via a downlink high-speed shared control channel (HS-SCCH). An uplink HS-DPCCH transfers uplink feedback signaling associated with a downlink HS-DSCH data transmission. A DPCH (dedicated physical channel) is a bidirectional physical channel to which a transport channel DCH is mapped. The DPCH is used to deliver dedicated data of a UE and L1 control information dedicated to a UE, such as a power control signal necessary for closed loop power control.
An F-DPCH (fractional dedicated physical channel) is a downlink channel for transferring several DPCHs using one channelization code. One F-DPCH does not transfer UE dedicated data for several UEs but rather is used to transfer UE-dedicated L1 control information for several UEs, such as the power control signal necessary for the closed loop power control. If the downlink F-DPCH exists, the downlink F-DPCH interfaces with an uplink DPCH. A plurality of UEs share the F-DPCH for use via one channel code. Each of the UEs is provided with an uplink DPCH.
FIG. 10 is a structural diagram of a sub-frame of HS-PDSCH according to the related art. A downlink HS-SCCH is a downlink physical channel transferred with a spreading factor set to 128 such that the data rate is 60 kbps. Information transferred over the downlink HS-SCCH can be classified into transport format and resource related information (hereinafter abbreviated TFRI) and HARQ related information. UE identity (H-RNTI) information, which indicates to which user the corresponding information belongs, is masked for transfer.
FIG. 11 is a flowchart of an HS-SCCH coding method according to the related art. HS-SCCH information for HS-SCCH coding is illustrated in Table TBD. HARQ and UE ID information is illustrated in Table II.
TABLE IChannelization-code-set information (7 bits): xccs 1, xccs 2, . . . , xccs 7Modulation scheme information (1 bit): xms 1Transport-block size information (6 bits): xtbs 1, xtbs 2, . . . , xtbs 6
TABLE IIHybrid-ARQ process information (3 bits): xhap 1, xhap 2, xhap 3Redundancy and constellation version (3 bits): xrv 1, xrv 2, xrv 3New data indicator (1 bit): xnd 1UE identity (16 bits): xue 1, xue 2, . . . , xue 16
FIG. 12 is a structural diagram of a frame of uplink HS-DPCCH according to the related art. An uplink HS-DPCCH transfers uplink feedback signaling associated with a downlink HS-DSCH data transmission.
The HS-DPCCH is a channel dedicated to a specific UE and interfaces with an uplink DPCH (dedicated physical channel) and a downlink DPCH (dedicated physical channel). The feedback signaling includes ACK (acknowledgement) or NACK (negative acknowledgement) information for HARQ and a CQI (channel quality indicator). A frame of the HS-DPCCH includes five sub-frames, each of which has a length of 2 ms. Each of the sub-frames includes three slots.
The ACK/NACK information for HARQ is transmitted for a first slot of the HS-DPCCH sub-frame. The CQI is transmitted for second and third slots of the HS-DSCH sub-frame.
The HS-DPCCH is always transmitted together with UL DPCCH. The CQI delivers status information of a downlink radio channel. The status information is obtained from a measurement of a downlink CPICH (common pilot channel) by a UE. The ACK/NACK indicates the ACK or NACK information for a user data packet transmission transmitted over a downlink HS-DSCH by the HARQ mechanism.
However, related art methods provide a maximum data rate for MBMS of only 256 Kbps, which corresponds to a maximum speed of one SCCPCH. Therefore, the related art methods are unable to provide an MBMS having a data rate greater than 256 Kbps. Furthermore, since an uplink channel for the MBMS is not provided, related art systems are unable to deliver information (ACK or NACK) in response to the MBMS transmission.
Therefore, there is a need for an apparatus and method to provide MBMS at a data rate greater than 256 Kbps and allow ACK/NACK information to be provided in response to the MBMS transmission. The present invention addresses these and other needs.